1. Field of the Invention
The present invention relates to a liquid crystal display device manufacturing method and a liquid crystal display device manufacturing system and, more particularly, a liquid crystal display device manufacturing method having the step of dropping a liquid crystal into a substrate from a syringe and a system used to manufacture the liquid crystal display device.
2. Description of the Prior Art
The liquid crystal display device has a structure that the TFT substrate on which the pixel electrodes, the thin film transistors (TFTs), etc. are formed and the opposed substrate on which the opposed electrode, the color filters, etc. are formed are stuck together, and the liquid crystal sealed between the TFT substrate and the opposed substrate.
As the method of sealing the liquid crystal between the TFT substrate and the opposed substrate, the vacuum injection method, the drop method, etc. are employed.
According to the vacuum injection method, an empty cell is formed by sticking two substrates to put a frame-like sealing member having a liquid crystal introducing port between them, then a space between the substrates is decompressed vacuous via the liquid crystal introducing port, and then the liquid crystal is introduced between the substrates by utilizing difference in the atmospheric pressure between the inside and the outside of the empty cell. According to the drop method, the liquid crystal is dropped down into the area of the TFT substrate, in which the sealing member is coated like the frame, and then the cell is formed by sticking the TFT substrate and the opposed substrate in the vacuum atmosphere.
In contrast to the vacuum injection method, the drop method has the merit such that no time is required to seal the liquid crystal introducing port of the frame-like sealing member and to clean the peripheral area of the liquid crystal introducing port. As the liquid crystal supply syringe employed in the drop method, there are the air system, the tubing system, the plunger system, etc., for example. Any one of these systems may be employed to drop the low-viscosity fluid such as the liquid crystal.
If the low-viscosity fluid is discharged minutely with high precision, normally the plunger system may be employed. In the plunger system, there are the capacity measuring type, the motor driving type, etc.
The syringe used in the plunger system has the structure shown in FIG. 1A. The operation for moving the plunger 102 in the syringe 101 in which the liquid crystal is filled is performed to drop the liquid crystal from the needle 103 provided to the lower end of the syringe 101 toward the substrate 104.
By the way, in the liquid crystal display device, in order to get the proper display, there exists the demand to seal an amount of liquid crystal with high precision.
However, if the minute liquid crystal 100 is discharged from the needle 103, in some cases the liquid crystal 100 adheres to the top of the needle 103, as shown in FIG. 1B, when the liquid crystal 100 is discharged or after the liquid crystal 100 is discharged.
If the adhered liquid crystal remains at the top of the needle, the precision in supplying the liquid crystal to the cell is lowered and thus the trouble occurs on the display.
Vacuum bubbles are mixed in the cell if a volume of the liquid crystal is reduced rather than the target volume, whereas the unusual cell thickness is brought about if a volume of the liquid crystal is increased rather than the target volume. If a supply amount of the liquid crystal to the liquid crystal display cell is reduced rather than the target volume, portions containing no liquid crystal appear as lines on the image. In contrast, if an amount of the liquid crystal is increased rather than the target volume, the liquid crystal display cell becomes inflated partially to cause the degradation of the image display. As the case where the liquid crystal is increased much more than the target volume, for example, there is the case that, when the supply of the liquid crystal to the n-th substrate (n; natural number) is finished, the liquid crystal adhered to the needle drops down onto the (n+1)-th substrate.
If the dropping speed of the liquid crystal from the equipment shown in FIG. 1A is increased, such adhesion of the liquid crystal onto the top of the needle can be eliminated. In this case, there is such a disadvantage that the discharge precision of the liquid crystal is lowered under such condition.